Photopolymerizable coating composition and process for forming a coating having a stereoscopic pattern

ABSTRACT

A photopolymerizable coating composition comprising: 
     (A) 100 parts by weight of a vehicle consisting essentially of a urethaneacrylate oligomer; 
     (B) from 0.1 to 5 parts by weight of an acylphosphine oxide compound as a photoinitiator; 
     (C) from 1 to 100 parts by weight of a color pigment; and 
     (D) from 20 to 300 parts by weight of a transparent glass powder having an average particle size of not larger than 100 μm and an index of refraction which does not differ more than 0.3 from the index of refraction of the composition excluding the color pigment.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a photopolymerizable coatingcomposition containing a color pigment, which is ultraviolet curable andwhich is capable of providing a coating layer excellent in the abrasionresistance and water resistance, and a process for forming a coating ofa stereoscopic pattern by using such a composition.

2. Discussion of Background

In recent years, photopolymerizable coating compositions containing nosolvent or little organic solvent have been employed in view of socialdemands for conservation of resources and pollution free operation.However, conventional photopolymerizable coating compositions are mainlyof a clear type containing no color pigment. An enamel type compositioncontaining a color pigment is practically used only in a limited areasince the coating thickness is limited, and its commercial developmentis stalemated.

As mentioned above, a photopolymerizable coating composition containinga color pigment has a difficulty in that when coated in a substantialthickness, ultraviolet rays will not sufficiently be transmitted to theinterior of the coating layer, whereby inadequate curing will result,and wrinkles are likely to form with the curing of only the surface ofthe layer, thus leading to a poor outer appearance of the coating layerFurther, the coating efficiency used to be poor.

Under these circumstances, it has been proposed to use as the colorpigment a pigment which hardly absorbs ultraviolet rays, or to use ahighly reactive photopolymerizable compound, or to use as theultraviolet lamp a lamp capable of emitting light rays of longwavelengths. However, in either proposal, the coating thickness islimited to a level of at most 30 μm. If the thickness exceeds thislimit, defective curing tends to result, and the coloring power and theopacifying power tend to be poor as compared with usual enamels.

Further, it has been recently proposed to incorporate spherical glassparticles to a photopolymerizable coating composition containing a colorpigment (e.g. Japanese Unexamined Patent Publication No. 79275/1987). Bythis method, it is possible to obtain a coating layer having thecurability improved to some extent. However, the composition is inferiorin the water resistance and exhibits poor curability by light rays withshort wavelengths.

On the other hand, as photoinitiators to be used for photopolymerizablecoating compositions, benzophenone, acetophenone, diethoxyacetophenone,chloroacetophenone, 2,2-dimethoxy-2-phenylacetophonone, propiophenone,thioxanthone, benzoin, benzyl, anthraquinone, benzylketal, benzoin ethylether, benzoin isopropyl ether and dimethoxyphenyl are known as typicalexamples (U.S. patent application Ser. Nos. 129,297, 731,888 and757,249). However, photoinitiators commonly employed including thosementioned above, are incapable of sufficiently curing the coating layersto the inside thereof if the photopolymerizable coating compositionscontaining them contain a substantial amount of an opacifying componentsuch as a color pigment.

Further, acylphosphine oxide compounds have been developed asphotoinitiators (U.S. Pat. Nos. 4,292,152 and 4,385,109). Thesecompounds are excellent in the photosensitivity as compared with theabove-mentioned photoinitiators and capable of forming cured coatinglayers even when used for photopolymerizable coating compositionscontaining color pigments. However, the coating thickness is stilllimited to a level of at most a few tens μm. If the coating thickness isat a level of a few hundreds μm, the inside of the coating layer willnot sufficiently be cured. Further, even in a case of a thin coatinglayer, if a large amount of a color pigment is incorporated to increasethe opacifying power, the curability tends to be poor, and the resultingcoating layer tends to be inferior in the water resistance, etc.

In the fields of interior decorating materials or building materials, ithas been common to employ materials having stereoscopic colorfulpatterns applied to present a beautiful outer appearance. Suchstereoscopic colorful patterns are usually applied by forming multiplecoating layers of different colors by (i) a gravure, offset or offsetgravure printing method, (ii) a screen printing method or (iii) acoating method, or by a combination of these methods. However, it iscommon to use an organic solvent for the coating material or for an inkused for such methods.

On the other hand, in view of the social demands for pollution freeoperation and conservation of resources, there has been in recent yearsa tendency of adopting a photopolymerizable coating compositioncontaining no solvent or a less amount of an organic solvent. Therefore,it is conceivable to use a photopolymerizable coating compositioncontaining no or little organic solvent, as the coating composition forforming such a stereoscopic colorful pattern. However, when such aphotopolymerizable coating composition is to be used as a coatingcomposition for forming a stereoscopic colorful pattern by multiplecoating layers, the coating composition is required to satisfy thefollowing conditions:

(1) It provides good intercoat adhesion when multiple coating layers areformed.

(2) It provides consistent curability within a wide light energy range.

(3) It provides constant curability even when the coating layerthickness varies.

(4) It is capable of maintaining the initial color of coating, which isnot affected even when irradiated several times with ultraviolet rays.

However, none of the conventional photopolymerizable coatingcompositions fully satisfies these conditions. Therefore, stereoscopiccolorful patterns formed by colored photopolymerizable coatingcompositions have not substantially practically used.

Namely, when a stereoscopic colorful pattern is formed by multiplecoating layers, the coating layer formed first i.e. the undercoatinglayer, is exposed several times to ultraviolet rays and accordingly willbe in an overcured state, whereby it is likely that the intercoatadhesion deteriorates or the layer undergoes a color change.

Further, the light emitting element of the ultraviolet curing apparatusis usually a tubular lamp, and the intensity of lights of the lamp inthe parallel direction is not constant. Particularly, the intensity oflights is low in the vicinity of the electrodes. Further, the lightintensity tends to decrease by the deterioration with time of the lamp.Under these conditions, the coating layer is likely to have a partialcuring defect, and a color change is likely to take place. Further, inthe case of ultraviolet curing, ultraviolet rays enter from the surfaceof the coating layer and reach to the boundary of the coating layer withthe substrate to complete the curing reaction However, it is usual thatthe thickness of the coating layer varies depending upon the nature ofthe coating composition such as the viscosity, the coating or printingconditions or the surface conditions of the substrate such as thesurface roughness of the substrate or the penetrability of the coatingcomposition. Consequently, it is likely that there will be some portionsdeep in the coating layer where the curing reaction is partiallyinadequate, and adhesion defects, blisters or wrinkles are likely toresult.

SUMMARY OF THE INVENTION

It is an object of the present invention to overcome the drawbacks ofthe conventional techniques and to provide a photopolymerizable coatingcomposition which is adequately curable by ultraviolet radiation evenwhen applied in a substantial thickness (e.g. a few hundreds μm) toprovide a coating layer which is excellent in the abrasion resistance,impact resistance, scratching resistance, flame retardancy, adhesion andwater resistance and which is capable of providing a coating layerhaving high opacifying power even in a thin layer since a color pigmentcan be incorporated in a large amount.

It is another object of the present invention to provide a process forforming a coating having a stereoscopic pattern, whereby a stereoscopicpattern composed of multiple coating layers can be formed with goodintercoat adhesion and in a short period of time by using certainspecific colored photopolymerizable coating compositions.

The present invention provides a photopolymerizable coating compositioncomprising:

(A) 100 parts by weight of a vehicle consisting essentially of aurethaneacrylate oligomer;

(B) from 0.1 to 5 parts by weight of an acylphosphine oxide compound asa photoinitiator;

(C) from 1 to 100 parts by weight of a color pigment; and

(D) from 20 to 300 parts by weight of a transparent glass powder havingan average particle size of not larger than 100 μm and an index ofrefraction which does not differ more than 0.3 from the index ofrefraction of the composition excluding the color pigment.

The present invention further provides a process for forming a coatinghaving a stereoscopic pattern, which comprises (a) forming a coloredundercoating layer on a substrate by coating the photopolymerizablecoating composition containing a color pigment over the entire surfaceor a part of the surface of the substrate followed by irradiation withultraviolet rays, and (b) forming a colored overcoating layer on theundercoating layer by coating the photopolymerizable coating compositioncontaining a color pigment having a color which is the same or differentfrom the color of the photopolymerizable coating composition for theundercoating layer, partially on the undercoating layer, followed byirradiation with ultraviolet rays.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to component (A), the vehicle consists essentially of aurethaneacrylate oligomer. The urethaneacrylate oligomer includesbroadly those having an urethane bond and a radical polymerizableunsaturated double bond in their molecules and having an averagemolecular weight of from a few hundreds to a few tens thousands, whichare viscous at room temperature.

For example, in addition to an oligomer obtainable by the reaction of apolyisocyanate with a (meth)acrylate having a hydroxyl group, apolyether type urethaneacrylate oligomer, a polyester typeurethaneacrylate oligomer and a polybutadiene type urethaneacrylateoligomer may be mentioned. Specifically, it may be a reaction product oftoluene diisocyanate, hexamethylene diisocyanate, isophoronediisocyanate, diphenylmethane diisocyanate, xylene diisocyanate, anisomer thereof, or a polyisocyanate (particularly preferably anon-yellowing type polyisocyanate) such as an isocyanate-terminatedcompound as a reaction product of an excess polyisocyanate with apolyhydric alcohol such as a polyester polyol, polyoxymethylene glycol,polyoxyethylene glycol, polyoxypropylene glycol, caprolactone polyol,trimethylolpropane or pentaerythritol, with a compound having a hydroxylgroup and an unsaturated group. As such a compound having a hydroxylgroup and an unsaturated group, hydroxypropyl (meth)acrylate,hydroxybutyl (meth)acrylate, hydroxyethyl (meth)acrylate or glycidyl(meth)acrylate may be mentioned as typical examples. A number ofvehicles are known to be useful for photopolymerizable coatingcompositions. Among them, a urethaneacrylate oligomer having goodinterlayer adhesion is used in the present invention.

The vehicle is composed of such a urethaneacrylate oligomer and areactive diluent. As such a reactive diluent, 2-ethylhexyl(meth)acrylate, 2-hydroxyethyl (meth)acrylate, isobornyl (meth)acrylate,tripropylene glycol diacrylate, 1,6-hexanediol diacrylate, tetraethyleneglycol diacrylate, trimethylolpropane tri(meth)acrylate, pentaerythritoltetra(meth)acrylate, ditrimethylolpropane pentaacrylate,dipentaerythritol hexaacrylate, vinyl acetate, N-vinylpyrrolidone,dimethyl (meth)acrylamide, vinyltoluene and divinylbenzene may bementioned as typical examples. Such a reactive diluent is incorporatedin an amount of from 10 to 100 parts by weight relative to 100 parts byweight of the urethaneacrylate oligomer.

Referring to component (B), an acylphosphine oxide compound is used asthe photoinitiator. The acylphosphine oxide compound may be a compoundof the formula I as disclosed in e.g. U.S. Pat. No. 4,385,109: ##STR1##wherein R¹ is alkyl of 1 to 6 carbon atoms, cycloalkyl of 5 or 6 ringcarbon atoms, aryl which is unsubstituted or substituted by halogen,alkyl or alkoxy, or a S-containing or N-containing five-membered orsix-membered heterocyclic radical,

R² has one of the meanings of R¹, but R¹ and R² may be identical ordifferent, or is alkoxy, aryloxy or aralkoxy, or R¹ and R² together forma ring, and

R³ is tertiary alkyl of 4 to 18 carbon atoms or tertiary cycloalkyl of 5or 6 ring carbon atoms or is a cycloalkyl, aryl or 5-membered or6-membered heterocyclic radical which contains substituents A and B atleast in the two positions ortho to the carbonyl group, A and B beingidentical or different and each being alkyl, alkoxy, alkoxyalkyl,alkylthio, cycloalkyl, aryl or halogen.

The phrase "which contains substituents A and B in the two positionsortho to the carbonyl group" means that the substituents A and B arebonded to the two ring carbon atoms, capable of substitution, which areadjacent to the point of attachment of the carbonyl group. This meansthat the α-naphthyl radical contains the substituents A and B at leastin the 2- and 8-positions and the β-naphthyl radical at least in the 1-and 3-positions. In the cyclohexyl radical, the substituents A and B arein the 2- and 6-positions, and in the cyclopentyl radical in the 2- and5-positions.

Examples of suitable acrylphosphine oxide compounds of the formula I foruse in the compositions according to the invention are:2,2-dimethyl-propionyldiphenylphosphine oxide,2,2-dimethyl-heptanoyldiphenylphosphine oxide,2,2-dimethyl-octanoyldiphenylphosphine oxide,2,2-dimethyl-nonanoyldiphenylphosphine oxide, methyl2,2-dimethyl-octanoylphenylphosphinate,2-methyl-2-ethyl-hexanoyldiphenylphosphine oxide,1-methyl-1-cyclohexanecarbonyldiphenylphosphine oxide,2,6-dimethylbenzoyldiphenylphosphine oxide,2,6-dimethoxybenzoyldiphenylphosphine oxide,2,6-dichlorobenzoyldiphenylphosphine oxide, methyl2,6-dimethoxybenzoylphenylphosphinate,2,4,6-trimethylbenzoyldiphenylphosphine oxide, methyl2,4,6-trimethylbenzoylphenylphosphinate,2,3,6-trimethylbenzoyldiphenylphosphine oxide,2,3,5,6-tetramethylbenzoyldiphenylphosphine oxide,2,4,6-trimethoxybenzoyldiphenylphosphine2,4,6-trichlorobenzoyldiphenylphosphine oxide,2-chloro-6-methylthio-benzoyldiphenylphosphine oxide, methyl2,4,6-trimethylbenzoylnaphthylphosphinate,1,3-dimethoxynaphthalene-2-carbonyldiphenylphosphine oxide,2,8-dimethoxynaphthalene-1-carbonyl-diphenylphosphine oxide,2,4,6-trimethylpyridine-3-carbonyl-diphenylphosphine oxide,2,4-dimethylquinoline-3-carbonyl-diphenylphosphine oxide,2,4-dimethoxyfuran-3-carbonyl-diphenylphosphine oxide and methyl2,4-dimethylfuran-3-carbonyl-phenylphosphine.

The acrylphosphine oxide compound is incorporated in an amount of from0.1 to 5 parts by weight, preferably from 0.2 to 3 parts by weight,relative to 100 parts by weight of the vehicle of component (A).

In some cases, conventional photoinitiators may be used in combinationwith the acylphosphine oxide compound as the photoinitiator of thepresent invention.

Referring to component (C), usual inorganic and organic pigments anddyestuffs may be used as the color pigment for the present invention.Specifically, titanium oxide, zinc sulfide, zinc white, white lead,lithopone, carbon black, lampblack, Berlin blue, phthalocyanine blue,ultramarine, carmine FB, chrome yellow, zinc yellow, Hanza Yellow,ochre, iron oxide red and an insoluble metal-containing azo dye may bementioned as typical examples. In the present invention, zinc sulfide,lampblack, ultramarine, phthalocyanine blue, carmine FB, chrome yellow,ochre, iron oxide red and an insoluble metal-containing azo dye areparticularly suitable as they have relatively small ultravioletabsorptivity.

Further, when it is desired to impart a metallic appearance to thecoating layer, a flaky metallic pigment, such as aluminum powder, copperpowder, stainless steel powder, mica powder, graphite powder or aplastic powder having gold, silver, copper or the like vapor-depositedthereto, may be used as the color pigment.

Likewise, when it is desired to impart a colorful dot appearance to thecoating layer, a colored powder coating material, colored plasticparticles, colored silica sand or colored pottery stone powder, may beused as the color pigment.

Further, when it is desired to impart electrical conductivity to thecoating layer, a powder of a metal such as gold, silver, copper, nickelor an alloy thereof, a powder of carbon black such as graphite, or apowder of an oxide, nitride or carbide of an element such as tin,titanium, zinc, aluminum, silicon, antimony or indium, may be employedas the color pigment.

Such a color pigment is incorporated in an amount of from 1 to 100 partsby weight, preferably from 1.5 to 85 parts by weight, relative to 100parts by weight of the vehicle of component (A). The amount of the colorpigment is usually not higher than 40% by weight in the formed coatinglayer, and the lower limit may optionally be determined depending uponthe desired opacifying power or coloring power of the coating layer.

As an extender pigment which may be incorporated as the case requires,silica sand, silicate, talc, kaolin, barium sulfate, calcium carbonate,flaky, fibrous or hollow glass and a powder of a resin such aspolyurethane, polyester, polyethylene or polystyrene, may be mentionedas typical examples.

Referring to component (D), the transparent glass powder has a functionto impart abrasion resistance to the formed coating layer and a functionto conduct the light energy to the interior of the coating layer,whereby it is possible to form a thick coating layer. Further, even inthe case of a thin coating layer, it is thereby possible to incorporatea large amount of the color pigment, whereby it is possible to form acoating layer having a high opacifying power.

In order to obtain the above-mentioned functions, the glass powder isrequired to satisfy the following conditions:

(a) The average particle size is not more than 100 μm, preferably from 3to 60 μm. Even if the average particle size exceeds 100 μm, there is nosubstantial effect to the curability of the coating layer, but the glasspowder is distinctly observed in the formed layer, and the surfaceroughness may result, such being undesirable from the viewpoint of theappearance of the coating layer. Further, there will be a deteriorationof the physical properties such as tensile strength. On the other hand,there is no particular restriction as to the lower limit of the particlesize. However, the transmittance tends to substantially decrease, andtherefore, the average particle size should preferably be within theabove-mentioned range.

(b) The index of refraction of the glass powder does not differ morethan 0.3 from the index of refraction of the clear coating layer of thephotopolymerizable coating composition excluding the color pigment. Ifthe difference in the index of refraction exceeds 0.3, the light energyfor curing the coating layer will substantially be attenuated inside thecoating layer when the coating layer is thick, whereby curing defect islikely to result.

When a coating film as thick as from a few tens μm to a few hundreds μmis to be formed, the glass powder is preferably spherical. Whereas, in acase where a thin coating layer at a level of a few μm to a few tens μmis to be formed, the glass powder is preferably non-specific shape.

There is no particular restriction as to the glass powder to be used inthe present invention, so long as the above conditions are satisfied.

The index of refraction N_(D) of a clear coating layer of aphotopolymerizable composition is usually from about 1.4 to 1.6.Accordingly, soda-lime glass, soda lime.lead glass, potassium.leadglass, potassium.lead glass, potassium.soda.lead glass, borosilicateglass, high alumina glass and potassium.soda.barium glass having anindex of refraction N_(D) of about 1.5 may be mentioned as specificexamples. However, the useful glass powder is not limited to suchspecific examples.

The glass powder is incorporated usually from 20 to 300 parts by weight,preferably from 30 to 200 parts by weight, relative to 100 parts byweight of the vehicle of component (A). The amount is usually from 20 to80% by weight in the formed coating layer. Particularly in the case of asingle coating layer having a thickness as thick as at least 100 μm, theamount of the glass powder is suitably from 30 to 70% by weight in thecoating layer.

Further, a solvent is usually employed to adjust the viscosity forcoating or printing. As such a solvent, toluene, xylene, acetone, methylethyl ketone or ethyl acetate may be mentioned as a typical example.

The colored photopolymerizable coating composition to be used in thepresent invention comprises the above described components.

The photopolymerizable coating composition of the present invention iscoated or printed on a substrate by using a usual coating or printingmeans and then ultraviolet rays are irradiated to induce thephotopolymerization reaction to cure the coating layer.

As the light source to be used for the irradiation of ultraviolet rays,a low pressure mercury lamp, a high pressure mercury lamp, a metalhalide lamp, a carbon arc lamp, a xenon lamp or a chemical lamp may beused.

The substrate to be coated may be of various types including metal,wood, plastic, glass, porcelain, concrete and paper substrates. Since itis possible to obtain a coating layer particularly excellent in theabrasion resistance, impact resistance, scratching resistance, flameretardancy and sound-shielding, the composition of the present inventionis useful particularly for interior decoration of buildings. Further,such a substrate may be the one subjected to preliminary treatment suchas filling treatment, sanding treatment or coloring treatment, or may bethe one having an uneven surface.

Now, a process for forming a coating having a stereoscopic patternaccording to the present invention will be described.

On the surface of a substrate as described above, the above-mentionedcolored photopolymerizable coating composition to form a coloredundercoating layer is coated or printed partially or entirely by acoating means such as a flow coater, a roll coater, a spray gun or apattern roller, or by a printing means such as gravure, offset, offsetgravure or screen printing.

Then, ultraviolet rays are irradiated to cure the colored undercoatinglayer.

In the case of a thick layer (e.g. from 100 to 500 μm), the ultravioletirradiation is conducted at a power input of at least 80 W/cm,preferably at least 120 W/cm. As the light source, the above-mentionedmetal halide lamp is particularly suitable. After curing the coloredundercoating layer, the above-mentioned colored photopolymerizablecoating composition having a color which is the same or different fromthe color of the undercoating layer is coated or printed by the samemeans as described above partially on the undercoating layer and/or onthe surface of the substrate where no undercoating layer has beenapplied.

Then, ultraviolet rays are irradiated to cure the colored overcoatinglayer. A multi-layered coating thus obtained has a stereoscopic pattern.When the colors of the respective layers are different, a stereoscopicmulti-colored pattern will be formed.

The process for forming a coating having a stereoscopic pattern has beendescribed with respect to a double-layered coating of a stereoscopicpattern. However, the coating may be a three or more multi-layeredcoating with a stereoscopic pattern. Further, a colored or colorlessclear coating layer may be applied as the outermost coating layer.

As described in the foregoing, the photopolymerizable coatingcomposition of the present invention contains the above-mentionedspecific vehicle component, the specific photoinitiator and the specificglass powder, and it is adequately curable with ultraviolet rays even ina thick coating layer at a level of a few hundreds pm (e.g. 500 μm),which used to be impossible in the case where a color pigment wasincorporated. Thus, it is possible to form a thick coating layer, whichhas high opacifying power and coloring power. Therefore, the compositionis epoch-making from the practical viewpoint. Further, in a case of athin coating layer at a level of from a few μm to a few tens μm, thecolor pigment can be incorporated in a large amount, whereby it ispossible to obtain a coating layer having a high opacifying power.Furthermore, since the glass powder is incorporated, the formed coatinglayer is excellent in the abrasion resistance, impact resistance,scratching resistance, flame retardancy, sound-shielding and adhesion.When subjected to ultraviolet irradiation, no heat will be created.Therefore, the present invention is applicable also to a substrate whichis generally weak to heat, and it is thereby possible to preventformation of wrinkles on the coating layer due to heat. Further, evenwhen a stereoscopic pattern is formed by multiple coating layers, theintercoat adhesion is excellent, and the composition has a constantcurability within a wide light energy range, whereby it is possible toobtain a coating with a stereoscopic pattern in a short period of timeand with a high coating performance.

Now, the present invention will be described in further detail withreference to Examples. However, it should be understood that the presentinvention is by no means restricted by such specific Examples. In theExamples, "parts" and "%" mean "parts by weight" and "% by weight".

Preparation of urethaneacrylate oligomer (I)

One mole of isophorone diisocyanate and 2 mols of 2-hydroxyethylacrylate were subjected to addition reaction by a usual method to obtainurethaneacrylate oligomer (I) having an average molecular weight ofabout 500.

Preparation of urethaneacrylate oligomer (II)

2.1 Mols of 1,6-hexanediol, one mol of ethylene glycol and 2.4 mols ofadipic acid were subjected to condensation reaction to obtain apolyester having a molecular weight of about 1,000. One mol of thispolyester, 2 mols of isophorone diisocyanate and 2 mols of2-hydroxyethyl acrylate were subjected to addition reaction by a usualmethod to obtain polyester-type urethaneacrylate oligomer (II) having anaverage molecular weight of about 1,700.

Preparation of epoxyacrylate oligomer (III)

One mol of a bisphenol A type diepoxy compound (Epikote 828, tradename,manufactured by Yuka Shell Epoxy Co., molecular weight: about 380) and 2mols of acrylic acid were subjected to addition reaction by a usualmethod to obtain epoxyacrylate oligomer (III) having an acid value of20.

Preparation of unsaturated polyester (IV)

One mol of maleic anhydride, one mol of phthalic anhydride and 2.1 molsof 1,2-propylene glycol were subjected to condensation reaction by ausual method to obtain an unsaturated polyester having an acid value of45 and an average molecular weight of about 8,000.

EXAMPLE 1

A photopolymerizable coating composition having the following blendcomposition was applied to a black-colored hard vinyl chloride resinplate by a 3 mil applicator and subjected to flash-off at 60° C for oneminute. Then, ultraviolet rays were irradiated for 2 seconds from adistance of 15 cm by a Fe.Sn halide lamp with 120 W/cm to cure thecoating layer. The obtained coating layer was tested for its properties.The results are shown in Table 1. The refractive index N_(D) of theclear coating layer of the composition having the soda glass powder andthe zinc sulfide pigment omitted from the blend composition, was 1.5.

    ______________________________________                                        Blend composition                                                             ______________________________________                                        Urethaneacrylate oligomer (I)                                                                           22    parts                                         N-vinylpyrrolidone        6     parts                                         2,4,6-trimethylbenzoyldiphenyl-                                                                         1     part                                          phosphine oxide                                                               Soda glass powder (transparent powder                                                                   40    parts                                         having a non-specific shape with a                                            refractive index N.sub.D of 1.52 and                                          an average particle size of 5 μm)                                          Zinc sulfide pigment      20    parts                                         n-Butyl acetate           11    parts                                         ______________________________________                                    

EXAMPLE 2

A coating layer was cured in the same manner as in Example 1 except thata photopolymerizable coating composition having the following blendcomposition was applied by a 10 mil applicator, and the ultraviolet rayswere irradiated for 2 seconds. The obtained coating layer was tested forits properties. The results are shown in Table 1. The refractive indexN_(D) of the clear coating layer of the composition having the sodaglass beads and the zinc sulfide pigment omitted from the blend

    ______________________________________                                        Blend composition                                                             ______________________________________                                        Urethaneacrylate oligomer (II)                                                                         25    parts                                          N-vinylpyrrolidone       7     parts                                          2,6-dimethoxybenzoyldiphenyl-                                                                          1     part                                           phosphine oxide                                                               Soda glass beads (transparent                                                                          55    parts                                          spherical beads with a refractive                                             index N.sub.D of 1.52 and an average                                          particle size of 60 μm)                                                    Zinc sulfide pigment     12    parts                                          ______________________________________                                    

COMPARATIVE EXAMPLE 1

The coating and ultraviolet irradiation were conducted under the sameconditions as in Example 1 except that instead of the soda glass powderin Example 1, a transparent lead glass powder having a non-specificshape with a refractive index N_(D) of 2.2 and an average particle sizeof 5 μm was used. The obtained coating layer was tested for itsproperties. The results are shown in Table 1.

COMPARATIVE EXAMPLE 2

The coating and ultraviolet irradiation were conducted under the sameconditions as in Example 1 except that the amount of the soda glasspowder in Example 1 was changed to 10 parts. The obtained coating layerwas tested for its properties. The results are shown in Table 1.

COMPARATIVE EXAMPLE 3

The coating and ultraviolet irradiation were conducted under the sameconditions as in Example 1 except that the amount of the soda glasspowder in Example 1 was changed to 300 parts. The obtained coating layerwas tested for its properties. The results are shown in Table 1.

COMPARATIVE EXAMPLE 4

The coating and ultraviolet irradiation were conducted under the sameconditions as in Example 2 except that in Example 2, soda glass beadshaving an average particle size of 111 pm were used. The obtainedcoating layer was tested for its properties. The results are shown inTable 1.

COMPARATIVE EXAMPLE 5

The coating and ultraviolet irradiation were conducted under the sameconditions as in Example 1 except that instead of the soda glass powderin Example 1, calcium carbonate was used as an extender pigment. Theobtained coating layer was tested for its properties. The results areshown in Table 1.

COMPARATIVE EXAMPLE 6

The coating and ultraviolet irradiation were conducted under the sameconditions as in Example 1 except that in Example 1, the zinc sulfidepigment was omitted, and instead of the glass powder, calcium carbonatewas used as an extender pigment. The obtained coating layer was testedfor its properties. The results are shown in Table 1. The obtainedcoating layer was a clear coating layer having turbidity.

COMPARATIVE EXAMPLE 7

The coating and ultraviolet irradiation were conducted under the sameconditions as in Example 1 except that instead of2,4,6-trimethylbenzoyldiphenylphosphine oxide in Example 1, anacetophenone photoinitiator was used. The obtained coating layer wastested for its properties. The results are shown in Table 1.

                                      TABLE 1                                     __________________________________________________________________________               Example No.                                                                             Comparative Example No.                                             1    2    1   2   3   4    5   6    7                              __________________________________________________________________________    Appearance of coating                                                                    O    O    O   O   X   Δ                                                                            O   O    O                              layer.sup.(1)                                                                 Abrasion resistance.sup.(2)                                                              350< 350< 350 100 350<                                                                              350< 100 100  350<                           Adhesion.sup.(3)                                                                         100/100                                                                            100/100                                                                            50/100                                                                            50/100                                                                            85/100                                                                            100/100                                                                            80/100                                                                            100/100                                                                            50/100                         Impact resistance.sup.(4)                                                                50 cm<                                                                             50 cm<                                                                             40 cm                                                                             10 cm                                                                             10 cm                                                                             40 cm                                                                              10 cm                                                                             10 cm                                                                              30 cm<                         Water resistance.sup.(5)                                                                 O    O    Δ                                                                           Δ                                                                           X   O    Δ                                                                           O    Δ                        __________________________________________________________________________     .sup.(1) Visual evaluation: O Good, Δ Roughened surface, X Roughene     surface with no gloss                                                         .sup.(2) An abrasivecoated paper was mounted on each of two rubber discs      of a Taber abrader, and the abrader was operated under a total load of 1      kg, whereby the number of rotations of the discs till the coating layer       was abraded to at least 50%, was taken as the abrasion resistance.            .sup.(3) Cross cut adhesion test.                                             .sup.(4) A drop weight of 500 g with a curvature radius of 1/2 inch was       dropped by a Dupont tester, whereby the falling height required to form a     crack by a single dropping operation, was taken as the impact resistance.     .sup.(5) The coated plate was immersed in water for one month: O No           change, Δ Blistering, X Peeling.                                   

EXAMPLE 3

A photopolymerizable coating composition having the following blendcomposition was applied in a thickness of 30 μm on a hard vinyl chlorideresin plate by an air spray and subjected to flash-off at 60° C. for oneminute. Then, the coated plate was passed under a metal halide lamp(power input: 120 W/cm) with a distance of 100 mm below the lamp at apassing speed of 15 m/min to cure the coating layer by the ultravioletradiation.

The obtained coated plate had a silver pearl-like metallic gloss. Evenafter it was immersed in water for one month, no abnormality such aspeeling or blistering of the coating layer, was observed. The refractiveindex N_(D) of the clear coating layer of the composition having thesoda glass beads and the mica powder omitted from the blend composition,was 1.5.

    ______________________________________                                        Blend composition                                                             ______________________________________                                        Urethaneacrylate oligomer (Unidic V4001,                                                                55    parts                                         tradename, manufactured by Dainippon                                          Ink Kagaku Kogyo K. K.)                                                       Dipentaerythritol hexaacrylate                                                                          30    parts                                         Titanium oxide-coated mica powder                                                                       15    parts                                         (Iriodin 130, tradename, E Merck Co.,                                         particle size: 15-130 μm)                                                  Soda glass beads (transparent                                                                           30    parts                                         spherical glass particles having an                                           average particle size of 10 μm and a                                       refractive index N.sub.D of 1.52)                                             2,6-Dichlorobenzoyl-diphenylphosphine                                                                   3     parts                                         oxide                                                                         Butyl acetate             10    parts                                         ______________________________________                                    

COMPARATIVE EXAMPLE 8

A coated plate was prepared in the same manner as in Example 3 exceptthat instead of the 2,6-dichlorobenzoyl-diphenylphosphine oxide inExample 3, α,α-dimethyl-α-hydroxyacetophenone was used as thephotoinitiator. The obtained coated plate had a cured coating layerhaving a silver pearl-like metallic gloss. However, when subjected to animmersion test in water for one month, the coating layer showed peelingand thus was poor in the water resistance. Likewise, the one whereinbenzophenone was used as the photoinitiator instead of the2,6-dichloro-benzoyl-diphenylphosphine oxide, showed peeling when it wassubjected to an immersion test in water.

COMPARATIVE EXAMPLE 9

A coated plate was prepared in the same manner as in Example 3 exceptthat the soda glass beads were omitted.

The coated plate thus obtained had a cured coating layer having a silverpearl-like metallic gloss. However, when subjected to an immersion testin water for one month, the coating layer showed blistering.

EXAMPLE 4

A photopolymerizable coating composition having the following blendcomposition was applied in a thickness of 40 μm on a soft vinyl chlorideresin plate by an applicator. Then, the coated layer was passed under ametal halide lamp (power input: 120 W/cm) with a distance of 100 mmbelow the lamp at a passing speed of 7.5 m/min to cure the coating layerby the ultraviolet radiation.

The coated plate thus obtained was soft, but black and had excellentabrasion resistance. The surface resistance was 5×10³ Ω/□, and thus thecoating layer had excellent electrical conductivity. Even after thecoated plated was immersed in water for one month, no abnormality suchas blistering or peeling of the coating layer, was observed.

    ______________________________________                                        Blend composition                                                             ______________________________________                                        Urethaneacrylate oligomer (II)                                                                         55    parts                                          N-vinylpyrrolidone       32    parts                                          Nickel powder (Carbonyl nickel                                                                         70    parts                                          powder 255, tradename, Nikko Fine                                             Product K. K., average particle                                               size: 2.5 μm)                                                              2,4,6-trimethylbenzoyldiphenyl                                                                         2     parts                                          phosphine oxide                                                               α,α-dimethyl-α-hydroxyacetophenone                                                   1     part                                           Soda glass beads (transparent                                                                          40    parts                                          spherical glass particles having an                                           average particle size of 10 μm and                                         a refractive index N.sub.D of 1.52)                                           ______________________________________                                    

COMPARATIVE EXAMPLE 10

A coated plate was prepared in the same manner as in Example 4 exceptthat the soda glass beads were omitted, and 3 parts ofα,α-dimethyl-α-hydroxyacetophenone was used alone as photoinitiator.

From its appearance, the coated plate thus obtained looked cured.However, the curing was poor inside, and the coating layer was readilypeeled.

EXAMPLE 5

By means of a 150 mesh direct printing screen having 100 square tilepatterns with a joint width of 4 mm, the white coating composition (I)as identified below was printed in a thickness of 50 μm on afilling-treated gray slate substrate by a urethane rubber squeegeehaving a hardness of 82°. Then, the printed substrate was passed under ametal halide lamp (power input: 120 W/cm) with a distance of 100 mmbelow the lamp to cure the coating layer by ultraviolet radiation. Thepassing speed was 3.7 m/min, and the integrated light volume was 1000mJ/cm² (as measured by an integrated radio meter UVPZ-1, manufactured byEye Graphics Co.).

Then, by means of a 30 mesh direct printing screen having stripepatterns harmonized to the above 100 square tile patterns, the blackcoating composition (II) as identified below was printed in a thicknessof 300 μm on the above screen-printed substrate by a urethane rubbersqueegee having a hardness of 82°, and the coating layer was cured underthe same condition as above. The finished coated substrate had astereoscopic multi-colored pattern with white 100 square tile patternshaving black stereoscopic stripe patterns on the gray joint lines.

With the coated plate, the substrate and the white coating layer, andthe white coating layer and the black coating layer were completelyintegral, and thus the adhesion was excellent.

ΔE of the white coating layer at the position where no black coatinglayer was overlaid, was 0.3 before and after the irradiation ofultraviolet rays to the black coating layer, thus indicating that thewhite coating layer underwent no substantial discoloration.

    ______________________________________                                        Colored photopolymerizable coating composition (I)                            ______________________________________                                        Urethaneacrylate oligomer (I)                                                                         22     parts                                          N-vinylpyrrolidone      6      parts                                          2,4,6-trimethylbenzoyldiphenyl-                                                                       0.6    part                                           phosphine oxide                                                               Soda glass beads (transparent                                                                         40     parts                                          spherical beads having an average                                             particle size of 10 μm and a                                               refractive index N.sub.D of 1.52)                                             Zinc sulfide            14     parts                                          Trimethylolpropane triacrylate                                                                        17.4   parts                                          ______________________________________                                    

The refractive index N_(D) of the clear coating layer of the compositionhaving the glass beads and the zinc sulfide omitted from the coatingcomposition (I), was 1.5.

    ______________________________________                                        Colored photopolymerizable coating composition (II)                           ______________________________________                                        Urethaneacrylate oligomer (II)                                                                         18.5   parts                                         1,6-Hexanediol diacrylate                                                                              15     parts                                         2,6-dimethoxybenzoyldiphenyl-                                                                          0.5    part                                          phosphine oxide                                                               Soda glass beads (transparent                                                                          55     parts                                         spherical beads having an average                                             particle size of 30 μm and a                                               refractive index N.sub.D of 1.52)                                             α,α-dimethyl-α-hydroxyacetophenone                                                   0.5    part                                          Calcium carbonate        10     parts                                         Carbon black             0.5    part                                          ______________________________________                                    

The refractive index N_(D) of the clear coating layer of the compositionhaving9 the glass beads, the calcium carbonate and the carbon blackomitted from the coating composition (II), was 1.5.

COMPARATIVE EXAMPLE 11

A multi-colored pattern was formed under the same conditions as inExample 5 except that in Example 5, the glass beads incorporated to thecoating composition (II) were changed to calcium carbonate granuleshaving the same particle size.

The coating layer of the black stripe patterns, cured only on itssurface, and the inside was viscous and noncured.

COMPARATIVE EXAMPLE 12

A stereoscopic multi-colored pattern was formed under the sameconditions as in Example 5 except that in Example 5, the photoinitiatorincorporated to the coating composition (II) was changed toα,α-dimethyl-α-hydroxyacetophenone only.

The inside of the coating layer of the black stripe patterns was notwell cured, whereby the adhesion with the white undercoating layer wasinferior.

COMPARATIVE EXAMPLE 13

A stereoscopic multi-colored pattern was formed under the sameconditions as in Example 5 except that the urethaneacrylate oligomer (I)incorporated to the coating composition (I) was changed to theepoxyacrylate oligomer (III).

The coating layer of the black stripe patterns was readily peeled by anadhesive tape, and the recoating properties were inferior.

COMPARATIVE EXAMPLE 14

A stereoscopic multi-colored pattern was formed under the sameconditions as in Example 5 except that the urethaneacrylate oligomer (I)incorporated to the coating composition (I) was changed to anunsaturated polyester (IV).

The layer of the black stripe patterns, was readily peeled by anadhesive tape, and the recoating properties were inferior.

Further, ΔE of the white coating layer before and after the irradiationof ultraviolet rays to the black coating layer, was 4.0, and the whitecoating layer underwent a color change to yellow.

What is claimed is:
 1. A photopolymerizable coating compositioncomprising:(A) 100 parts by weight of a vehicle consisting essentiallyof a urethaneacrylate oligomer; (B) from 0.1 to 5 parts by weight of anacylphosphine oxide compound as a photoinitiator; (C) from 1 to 100parts by weight of a color pigment; and (D) from 20 to 300 parts byweight of a transparent glass powder having an average particle size ofnot larger than 100 μm and an index of refraction which does not differmore than 0.3 from the index of refraction of the composition excludingthe color pigment.
 2. The photopolymerizable coating compositionaccording to claim 1, wherein the glass powder has an average particlesize of from 3 to 60 μm.
 3. The photopolymerizable coating compositionaccording to claim 1, wherein the vehicle consists essentially of 100parts by weight of the urethaneacrylate oligomer and from 10 to 100parts by weight of a reactive diluent selected from the group consistingof 2 ethylhexyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, isobornyl(meth)acrylate, tripropylene glycol diacrylate, 1,6-hexanedioldiacrylate, tetraethylene glycol diacrylate, trimethylolpropanetri(meth)acrylate, pentaerythritol tetra(meth)acrylate,ditrimethylolpropane pentaacrylate, dipentaerythritol hexaacrylate,vinyl acetate, N-vinyl pyrrolidone, dimethyl (meth)acrylamide, vinyltoluene and divinylbenzene.
 4. The photopolymerizable coatingcomposition according to claim 1, wherein the acylphosphine oxidecompound is a compound of the formula: ##STR2## wherein R¹ is alkyl of 1to 6 carbon atoms, cycloalkyl of 5 or 6 ring carbon atoms, aryl which isunsubstituted or substituted by halogen, alkyl or alkoxy, or aS-containing or N-containing five-membered or six-membered heterocyclicradical,R² has one of the meanings of R¹, but R¹ and R² may be identicalor different, or is alkoxy, aryloxy or aralkoxy, or R¹ and R² togetherform a ring, and R³ is tertiary alkyl of 4 to 18 carbon atoms ortertiary cycloalkyl of 5 or 6 ring carbon atoms or is a cycloalkyl, arylor 5-membered or 6-membered heterocyclic radical which containssubstituents A and B at least in the two positions ortho to the carbonylgroup, A and B being identical or different and each being alkyl,alkoxy, alkoxyalkyl, alkylthio, cycloalkyl, aryl or halogen.
 5. Thephotopolymerizable coating composition according to claim 1, wherein thecolor pigment is selected from the group consisting of titanium oxide,zinc sulfide, zinc white, white lead, lithopone, carbon black, lampblack, Berlin blue, phthalocyanine blue, ultramarine, carmine FB, chromeyellow, zinc yellow, Hanza Yellow, ochre, iron oxide red and aninsoluble metal containing azo dye.
 6. The photopolymerizable coatingcomposition according to claim 1, wherein the color pigment is selectedfrom the group consisting of aluminum powder, copper powder, stainlesssteel powder, mica powder, graphite powder and a plastic powder havinggold, silver or copper vapor-deposited thereto.
 7. Thephotopolymerizable coating composition according to claim 1, wherein thecolor pigment is selected from the group consisting of colored powdercoating material, colored plastic particles, colored silica sand andcolored pottery stone powder.
 8. The photopolymerizable coatingcomposition according to claim 1, wherein the color pigment is anelectrically conductive material selected from the group consisting ofmetal powder, carbon black powder and powders of oxides, nitrides andcarbides of tin, titanium, zinc, aluminum, silicon, antimony and indium.9. The photopolymerizable coating composition according to claim 1,wherein the glass powder is a powder of soda-lime glass, soda-lime.leadglass, potassium.lead glass, potassium.soda.lead glass, borosilicateglass, high alumina glass or potassium.soda.barium glass.
 10. A processfor forming a coating having a stereoscopic pattern, which comprises (a)forming a colored undercoating layer on a substrate by coating aphotopolymerizable coating composition of claim 1 containing a colorpigment over the entire surface or a part of the surface of thesubstrate, followed by irradiation with ultraviolet rays, and (b)forming a colored overcoating layer on the undercoating layer by coatinga photopolymerizable coating composition of claim 1 containing a colorpigment having a color which is the same or different from the color ofthe photopolymerizable coating composition for the undercoating layer,partially on the undercoating layer, followed by irradiation withultraviolet rays.